OFDMA with block tone assignment for WLAN

ABSTRACT

An access point (AP) device assigns respective blocks of orthogonal frequency division multiplexing (OFDM) tones to a plurality of client stations for an orthogonal frequency division multiple access (OFDMA) data unit. The AP device receives respective independent data for the plurality of client stations, and generates a preamble of the OFDMA data unit to include: respective legacy preamble portions in respective sub-channels. Each legacy preamble portion includes a legacy signal field that indicates a duration of the OFDMA data unit, and a non-legacy preamble portion. The AP device also generates a data portion of the OFDMA data unit to include respective independent data for respective client stations. The respective independent data are included within the respective blocks of OFDM tones.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/924,573, now U.S. Pat. No. 10,462,790, entitled “OFDMA with BlockTone Assignment for WLAN,” filed on Mar. 19, 2018, which is acontinuation of U.S. patent application Ser. No. 14/730,651, now U.S.Pat. No. 9,924,512, entitled “OFDMA with Block Tone Assignment forWLAN,” filed on Mar. 24, 2010, which claims the benefit of U.S.Provisional Patent Application No. 61/162,780, entitled “Simple OFDMAwith Block Tone Assignment for WLAN,” filed on Mar. 24, 2009. Thedisclosures of the applications referenced above are incorporated byreference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, and the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps.

These WLANs operate in either a unicast mode or a multicast mode. In theunicast mode, the AP transmits information to one client station at atime. In the multicast mode, the same information is transmitted to agroup of client stations concurrently.

SUMMARY

In an embodiment, a method for transmitting to a plurality of clientstations in a wireless local area network (WLAN) includes: assigning, atan access point (AP) device, respective blocks of orthogonal frequencydivision multiplexing (OFDM) tones to the plurality of client stationsfor an orthogonal frequency division multiple access (OFDMA) data unit;receiving, at the AP device, respective independent data for theplurality of client stations; and generating, at the AP device, apreamble of the OFDMA data unit to include: respective legacy preambleportions in respective sub-channels, wherein each legacy preambleportion includes a legacy signal field that indicates a duration of theOFDMA data unit, and a non-legacy preamble portion. The method alsoincludes: generating, at the AP device, a data portion of the OFDMA dataunit to include respective independent data for respective clientstations, the respective independent data included within the respectiveblocks of OFDM tones; and transmitting, by the AP device, the OFDMA dataunit.

In another embodiment, a wireless communication device comprises: a WLANnetwork interface device associated with an AP device of a WLAN. TheWLAN network interface device comprises one or more integrated circuit(IC) devices, and one or more transceivers. The one or more IC devicesare configured to: assign respective blocks of OFDM tones to theplurality of client stations for an OFDMA data unit, and receiverespective independent data for the plurality of client stations. Theone or more IC devices are configured to generate a preamble of theOFDMA data unit to include: a respective legacy preamble portion in eachsub-channel of a plurality of subchannels, wherein each legacy preambleportion includes a legacy signal field that indicates a duration of theOFDMA data unit, and a non-legacy preamble portion. The one or more ICdevices are further configured to: generate a data portion of the OFDMAdata unit to include respective independent data for respective clientstations, the respective independent data included within the respectiveblocks of OFDM tones; and control the one or more transceivers totransmit the OFDMA data unit.

In yet another embodiment, a method for communicating with a pluralityof client stations in a WLAN includes: transmitting, by an AP device ofa WLAN, a synchronization signal to prompt a plurality of clientstations of the WLAN to transmit as part of an uplink OFDMA transmissionat a time that begins a defined time period after an end of thesynchronization signal; and subsequent to transmitting thesynchronization signal, receiving, at the AP device, the uplink OFDMAtransmission from the plurality of client stations, wherein the OFDMAtransmission is responsive to the synchronization signal. The uplinkOFDMA transmission includes: respective legacy preamble portions inrespective sub-channels, wherein each legacy preamble portion includes alegacy signal field that indicates a duration of the uplink OFDMAtransmission, a non-legacy preamble portion, and respective independentdata from respective client stations among the plurality of clientstations, the respective independent data included within respectiveblocks of orthogonal frequency division multiplex (OFDM) tones.

In still another embodiment, a wireless communication device comprises:a WLAN network interface device associated with an AP device of a WLAN.The WLAN network interface device comprises: one or more integratedcircuit (IC) devices, and one or more transceivers. The one or more ICdevices are configured to: control the one or more transceivers totransmit a synchronization signal to prompt a plurality of clientstations of a WLAN to transmit as part of an uplink OFDMA transmissionat a time that begins a defined time period after an end of thesynchronization signal. The WLAN network interface device is furtherconfigured to: subsequent to transmitting the synchronization signal,receive the uplink OFDMA transmission from the plurality of clientstations, wherein the OFDMA transmission is responsive to thesynchronization signal. The uplink OFDMA transmission includes:respective legacy preamble portions in respective sub-channels, whereineach legacy preamble portion includes a legacy signal field thatindicates a duration of the uplink OFDMA transmission, a non-legacypreamble portion, and respective independent data from respective clientstations among the plurality of client stations, the respectiveindependent data included within respective blocks of orthogonalfrequency division multiplex (OFDM) tones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a block diagram of an example wireless local area network (WLAN)10, according to an embodiment;

FIGS. 2A, 2B, and 2C are diagrams illustrating example orthogonalfrequency division multiplexing (OFDM) sub-channel blocks for an 80 MHzcommunication channel, according to an embodiment;

FIG. 3 is a diagram of an OFDM symbol that is partitioned into threeOFDM sub-channel blocks for an 80 MHz communication channel;

FIG. 4 is a block diagram of an example downlink orthogonal frequencydivision multiple access (OFDMA) signal, according to an embodiment;

FIG. 5 is a block diagram of an example downlink OFDMA signal, accordingto another embodiment;

FIG. 6 is a diagram illustrating the transmission of a downlink OFDMAdata unit by an access point (AP), and the transmission ofacknowledgment signals (ACKs) by client stations in response to thedownlink OFDMA data unit, according to an embodiment;

FIG. 7 is a diagram illustrating the transmission of a downlink OFDMAdata unit by an AP, and the transmission of ACKs by client stations inresponse to the downlink OFDMA data unit, according to anotherembodiment;

FIG. 8 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment;

FIG. 9 is a flow diagram of another example method that is implementedby an AP in a WLAN, according to an embodiment;

FIG. 10 is a block diagram of an example physical layer (PHY) unit of anAP, according to an embodiment;

FIG. 11 is a block diagram of an example physical layer (PHY) unit of anAP, according to another embodiment;

FIG. 12 is a diagram illustrating communications in a WLAN duringcarrier sense multiple access (CSMA) time periods and an OFDMA timeperiod, according to an embodiment;

FIG. 13 is a diagram illustrating the transmission of an uplink OFDMAdata unit by a plurality of client stations, and the transmission ofACKs by the AP in response to the uplink OFDMA data unit, according toan embodiment;

FIG. 14 is a diagram illustrating the transmission of an uplink OFDMAdata unit being preceded by the AP transmitting downlink synchronizationsignals 520, according to an embodiment;

FIG. 15 is a diagram illustrating communications in a WLAN during CSMAtime periods and an OFDMA time period, according to an embodiment;

FIG. 16 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment; and

FIG. 17 is a flow diagram of another example method that is implementedby an AP in a WLAN, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmitsindependent data streams to multiple client stations simultaneously. Inparticular, the wireless device utilizes orthogonal frequency divisionmultiplexing (OFDM) and transmits data for the multiple clients indifferent blocks of OFDM subchannels. Similarly, in embodimentsdescribed below, multiple client stations transmit data to an APsimultaneously, in particular, each client station utilizes OFDM andtransmits data to the AP in a different block of OFDM subchannels.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) unit 18 and a physical layer(PHY) unit 20. The PHY unit 20 includes a plurality of transceivers 21,and the transceivers are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Additionally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 receives the data streamssimultaneously.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC unit 28 and a PHYunit 29. The PHY unit 29 includes a plurality of transceivers 30, andthe transceivers are coupled to a plurality of antennas 34. Althoughthree transceivers 30 and three antennas 34 are illustrated in FIG. 1,the client station 25-1 can include different numbers (e.g., 1, 2, 4, 5,etc.) of transceivers 30 and antennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas, according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation that is not enabled to receive a data stream that is transmittedby the AP 14 simultaneously with other independent data streams that areintended for other client stations 25. Similarly, according to anembodiment, the legacy client station 25-4 is not enabled to transmit adata stream that to the AP 24 at the same time that other clientstations 25 transmit data to the AP 14. According to an embodiment, thelegacy client station 25-4 includes a PHY unit that is generally capableof receiving a data stream that is transmitted by the AP 14simultaneously with other independent data streams that are intended forother client stations 25. But the legacy client station 25-4 includes aMAC unit that is not enabled with MAC layer functions that supportreceiving the data stream that is transmitted by the AP 14simultaneously with other independent data streams that are intended forother client stations 25. According to an embodiment, the legacy clientstation 25-4 includes a PHY unit that is generally capable oftransmitting a data stream to the AP 14 at the same time that otherclient stations 25 transmit data to the AP 14. But the legacy clientstation 25-4 includes a MAC unit that is not enabled with MAC layerfunctions that support transmitting a data stream to the AP 14 at thesame time that other client stations 25 transmit data to the AP 14.

In an embodiment, the legacy client station 25-4 operates according tothe IEEE 802.11a and/or the IEEE 802.11n Standards. The legacy clientstation 25-4, when it communicates with the AP 14, occupies an entirecommunication channel. For example, the IEEE 802.11a Standard definescommunication channels each having a width of 20 MHz. When the AP 14 andthe legacy client station 25-4 communicate according to the IEEE 802.11aStandard, the AP 14 transmits data to the legacy client station 25-4 in64 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 64 OFDMsubchannels. The IEEE 802.11n Standard defines 20 MHz and 40 MHzcommunications channels. When the AP 14 and the legacy client station25-4 communicate according to the IEEE 802.11n Standard using a 20 MHzchannel, the AP 14 transmits data to the legacy client station 25-4 in64 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 64 OFDMsubchannels. When the AP 14 and the legacy client station 25-4communicate according to the IEEE 802.11n Standard using a 40 MHzchannel, the AP 14 transmits data to the legacy client station 25-4 in128 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 128 OFDMsubchannels.

According to the IEEE 802.11a and the IEEE 802.11n Standards, differentdevices share the communication channel by utilizing a carrier sense,multiple access (CSMA) protocol. Generally speaking, CSMA, according tothe IEEE 802.11a and the IEEE 802.11n Standards, specifies that a devicethat wishes to transmit should first check whether another device in theWLAN is already transmitting. If another device is transmitting, thedevice should wait for a time period and then again check again to seewhether the communication channel is being used. If a device detectsthat the communication channel is not being used, the device thentransmits using the channel. With CSMA, in other words, data that is fora particular device (i.e., not multicast data) can only be transmittedon the channel when no other data is being transmitted on the channel.

According to an embodiment, the AP 14 is enabled to transmit differentdata streams to different client stations 25 at the same time. Inparticular, the PHY unit 20 is configured to transmit in a communicationchannel that is wider than specified by the IEEE 802.11a and the IEEE802.11n Standards. For example, the PHY unit 20 is configured totransmit in one or more of an 80 MHz communication channel, a 120 MHzcommunication channel, and/or a 160 MHz communication channel, accordingto an embodiment. As another example, the PHY unit 20 is additionallyconfigured to transmit in one or more of a 200 MHz communicationchannel, a 240 MHz communication channel, a 280 MHz communicationchannel, etc., according to an embodiment.

According to an embodiment, the AP 14 is configured to partition thewider communication channel into narrower sub-bands or OFDM sub-channelblocks, and different data streams for different client devices 25 aretransmitted in respective OFDM sub-channel blocks. According to anembodiment, each OFDM sub-channel block substantially conforms to thePHY specification of the IEEE 802.11a Standard. According to anotherembodiment, each OFDM sub-channel block substantially conforms to thePHY specification of the IEEE 802.11n Standard. According to anotherembodiment, each OFDM sub-channel block substantially conforms to a PHYspecification of a communication protocol other than the IEEE 802.11aand the IEEE 802.11n Standards.

As used herein, the phrase “OFDM sub-channel block substantiallyconforms to the PHY specification” of a communication protocol orstandard generally means that a device (configured according to thecommunication protocol or standard) that receives the transmitted OFDMsub-channel block is able, generally, to detect and decode the data inthe OFDM sub-channel block (signal strength, signal-to-noise (SNR),interference, etc., permitting). For example, an OFDM sub-channel blockthat substantially conforms to the PHY specification of a communicationprotocol or standard utilizes the modulation, tone mapping, pilotlocations, etc., set forth in the communication protocol or standard,although other aspects of the OFDM sub-channel block do not conform tothe PHY specification, according to an embodiment. For example, theremay be more zero tones at the edges of an OFDM sub-channel block,reduced power (by frequency domain power allocation) at edge tones,etc., than called for by the communication protocol or standard.Similarly, a used herein, the phrase “a device configured tosubstantially conform to the PHY specification” of a communicationprotocol or standard generally means that the device is able to detectand decode a signal that conforms or an OFDM sub-channel block thatsubstantially conforms to the communication protocol or standard (signalstrength, signal-to-noise (SNR), interference, etc., permitting). Thephrase “a device configured to substantially conform to the PHYspecification” of a communication protocol or standard also generallymeans that the device is able to generate a signal that conforms or anOFDM sub-channel block that substantially conforms to the communicationprotocol or standard.

When an OFDM sub-channel block substantially conforms to the PHYspecification of the IEEE 802.11a Standard, for example, a client device25 corresponding to the OFDM sub-channel block utilizes a PHY unit 29configured (or substantially configured) according to the IEEE 802.11aStandard to receive the data stream transmitted in the OFDM sub-channelblock. When an OFDM sub-channel block substantially conforms to the PHYspecification of the IEEE 802.11n Standard, for example, a client device25 corresponding to the OFDM sub-channel block utilizes a PHY unit 29configured (or substantially configured) according to the IEEE 802.11nStandard to receive the data stream transmitted in the OFDM sub-channelblock.

According to an embodiment, each OFDM sub-channel block includes acontiguous block of OFDM sub-channels or tones that can be demodulatedat the client station using a fast Fourier transform (FFT) with a widththe size of the OFDM sub-channel block. In other words, according tothis embodiment, the OFDM sub-channels assigned to client stations arenot interleaved such as in the Wi-Max standard.

FIGS. 2A, 2B, and 2C are diagrams illustrating example OFDM sub-channelblocks for an 80 MHz communication channel, according to an embodiment.In FIG. 2A, the communication channel is partitioned into fourcontiguous OFDM sub-channel blocks, each having a bandwidth of 20 MHz.The OFDM sub-channel blocks include independent data streams for fourclient stations. In FIG. 2B, the communication channel is partitionedinto two contiguous OFDM sub-channel blocks, each having a bandwidth of40 MHz. The OFDM sub-channel blocks include independent data streams fortwo client stations. In FIG. 2C, the communication channel ispartitioned into three contiguous OFDM sub-channel blocks. Two OFDMsub-channel blocks each have a bandwidth of 20 MHz. The remaining OFDMsub-channel block has a bandwidth of 40 MHz. The OFDM sub-channel blocksinclude independent data streams for three client stations.

Although in FIGS. 2A, 2B, and 2C, the OFDM sub-channel blocks arecontiguous across the communication channel, in other embodiments theOFDM sub-channel blocks are not contiguous across the communicationchannel (i.e., there are one or more gaps between the OFDM sub-channelblocks). In an embodiment, each gap is at least as wide as one of theOFDM sub-channel blocks. In another embodiment, at least one gap is lessthan the bandwidth of an OFDM sub-channel block. In another embodiment,at least one gap is at least as wide as 1 MHz. In an embodiment,different OFDM sub-channel blocks are transmitted in different channelsdefined by the IEEE 802.11a and/or 802.11n Standards. In one embodiment,the AP includes a plurality of radios and different OFDM sub-channelblocks are transmitted using different radios.

In an embodiment, for a plurality of data streams transmitted by an APin different OFDM sub-channel blocks, different data streams aretransmitted at different data rates when, for example, signal strength,SNR, interference power, etc., varies between client devices.Additionally, for a plurality of data streams transmitted by an AP indifferent OFDM sub-channel blocks, the amount of data in different datastreams is often different. Thus, one transmitted data stream can endbefore another. In such situations, the data in an OFDM sub-channelblock corresponding to data stream that is ended is set to zero or someother suitable predetermined value, according to an embodiment. FIG. 3is a diagram of an (n+1)-th OFDM symbol that is partitioned into threecontiguous OFDM sub-channel blocks for an 80 MHz communication channel.Two OFDM sub-channel blocks, corresponding to a Station 1 and a Station3 each have a bandwidth of 20 MHz. The remaining OFDM sub-channel block,corresponding to a Station 2, has a bandwidth of 40 MHz. The OFDMsub-channel blocks include independent data streams for the threestations. The data stream corresponding to Station 2 ended in the n-thOFDM symbol (i.e., the OFDM symbol previous to the (n+1)-th OFDMsymbol), whereas the data streams corresponding to Station 1 and Station2 have not yet ended. Thus, for the (n+1)-th OFDM symbol, data in theOFDM sub-channel block corresponding to a Station 2 is set to zero.

An OFDM signal comprising a plurality of OFDM sub-channel blocks totransmit independent data streams as described above is also referred toherein as an orthogonal frequency division multiple access (OFDMA)signals. According to an embodiment, a WLAN utilizes downlink OFDMAsignals and uplink OFDMA signals. Downlink OFDMA signals are transmittedsynchronously from a single AP to multiple client stations (i.e.,point-to-multipoint). An uplink OFDMA signal is transmitted by multipleclients stations jointly to a single AP (i.e., multipoint-to-point).Frame formats and/or signaling schemes for downlink OFDMA and uplinkOFDMA are different, according to some embodiments.

Embodiments of a PHY frame format for downlink OFDMA signals will now bedescribed. In the following embodiments, OFDM sub-channel blocks have aformat substantially similar to the PHY format specified in the IEEE802.11n Standard. In other embodiments, OFDM sub-channel blocks have aformat substantially similar to another communication protocol such asthe PHY format specified in the IEEE 802.11a Standard or a communicationprotocol not yet standardized.

FIG. 4 is a block diagram of an example downlink OFDMA signal 100,according to an embodiment, that is partitioned into four equal-widthOFDM sub-channel blocks 102 corresponding to four client stations. Inthe embodiment of FIG. 4, each OFDM sub-channel block 102 has a formatsubstantially similar to the “mixed mode” data unit PHY format specifiedin the IEEE 802.11n Standard. For example, each OFDM sub-channel blockincludes a preamble 104 including a legacy short training field (L-STF),a legacy long training field (L-LTF), a legacy signal (L-SIG) field, ahigh throughput signal (HT-SIG) field, a high throughput short trainingfield (HT-STF), and one or more high throughput long training fields(HT-LTF). Additionally, each OFDM sub-channel block includes a highthroughput data field 108 (HT-DATA). The duration of the high throughputportion of the downlink OFDMA signal 100 is T, which corresponds to thelongest of the four OFDM sub-channel blocks 102 (i.e., 102-4). In otherwords, the durations of the high throughput portions of the OFDMsub-channel blocks 102-1, 102-2, and 102-3 are shorter than the durationof the high throughput portion of the downlink OFDMA signal 100.

The legacy portion of the preamble 104 (i.e., L-STF, L-LTF, and L-SIG)is identical in all of the OFDM sub-channel blocks 102, according to anembodiment. For the high throughput portion of the preamble 104 (i.e.,starting with HT-SIG), the content of the OFDM sub-channel blocks 102can be variant for different client stations depending on factors suchas rate, data quantity, configuration (e.g., number of antennas, numberof supported multiple input, multiple output (MIMO) data streams, etc.)of different clients.

According to an embodiment, the AP sets the “reserved bit” in each ofthe L-SIG fields to “1” (the IEEE 802.11a and 802.11n Standards specifythat the “reserved bit” in L-SIG to “0”) to signal the receiver that thecurrent data unit is a downlink OFDMA signal. Additionally, the AP setsthe Length and Rate sub-fields in each off the L-SIG fields tocorrespond to T, the duration of the high throughput portion of thelongest OFDM sub-channel block 102 (i.e., 102-4). According to anotherembodiment, the AP sets the “reserved bit” in each of the HT-SIG fieldsto “0” (the IEEE 802.11n Standard specifies that the “reserved bit” inHT-SIG to “1”) to signal the receiver that the current data unit is adownlink OFDMA signal.

In other embodiments, the AP signals that a data unit is a downlinkOFDMA signal using techniques other than those described above. Forexample, according to one embodiment, the AP uses MAC layer signaling toreserve a time period for transmitting a downlink OFDMA signal. In thisembodiment, MAC layer signaling is utilized to specify the duration T ofthe downlink OFDMA signal 100. In another embodiment, MAC layersignaling does not specify the duration T of the downlink OFDMA signal100, but rather specifies different respective times at which respectiveclient stations should send respective acknowledgments of the downlinkOFDMA signal 100. In another embodiment, the AP utilizes MAC layersignaling to specify a single time at which all client stationscorresponding to the downlink OFDMA signal 100 should simultaneouslytransmit respective acknowledgments.

In one embodiment, each OFDM sub-channel block 102 in FIG. 4 has a widthof 20 MHz. In another embodiment, each OFDM sub-channel block 102 inFIG. 4 has a width of 40 MHz. According to an embodiment, if an OFDMsub-channel block has a width of 40 MHz, the legacy portion of thepreamble 104 (i.e., L-STF, L-LTF, and L-SIG) is duplicated at upper andlower 20 MHz halves, with the sub-channels in the upper 20 MHz phaseshifted by 90 degrees with respect to the sub-channels in the lower 20MHz.

FIG. 5 is a block diagram of an example downlink OFDMA signal 150,according to an embodiment, that is partitioned into four equal-widthOFDM sub-channel blocks 152 corresponding to four client stations. Inthe embodiment of FIG. 5, each OFDM sub-channel block 152 has a formatsubstantially similar to the “Green field mode” data unit PHY formatspecified in the IEEE 802.11n Standard. For example, each OFDMsub-channel block includes a preamble 154 including an HT-SIG field, andHT-STF field, and one or more HT-LTF fields. Additionally, each OFDMsub-channel block 152 includes a high throughput data field 158(HT-DATA). The duration of the downlink OFDMA signal 100 is T. Theduration of each OFDM sub-channel block 152 is also T. In other words,the AP controls the duration of each OFDM sub-channel block 152 to be T,according to an embodiment. In one embodiment, the AP utilizes zeropadding to ensure that each OFDM sub-channel block 152 has a duration ofT. In one embodiment, a MAC unit of the AP zero pads one or more MACservice data units (MSDUs) that are included in a MAC protocol data unit(MPDU), which is in turn included in a PHY protocol data unit (PPDU). Byzero padding an MSDU, for example, the lengths of the MPDU and the PPDUare increased.

In an embodiment, the AP uses MAC layer signaling to reserve a timeperiod for transmitting the downlink OFDMA signal 150. In oneembodiment, MAC layer signaling is utilized to specify the duration T ofthe downlink OFDMA signal 150. In another embodiment, MAC layersignaling does not specify the duration T of the downlink OFDMA signal150, but rather specifies different respective times at which respectiveclient stations should send respective acknowledgments of the downlinkOFDMA signal 150. In another embodiment, the AP utilizes MAC layersignaling to specify a single time at which all client stationscorresponding to the downlink OFDMA signal 150 should simultaneouslytransmit respective acknowledgments.

In another embodiment, a downlink OFDMA signal includes one or more OFDMsub-channel blocks that have a format substantially similar to the“mixed mode” data unit PHY format specified in the IEEE 802.11n Standardand one or more OFDM sub-channel blocks that have a format substantiallysimilar to the “Green field mode” data unit PHY format specified in theIEEE 802.11n Standard. In one implementation, the AP forms the downlinkOFDMA signal so that the duration of each of the OFDM sub-channel blocksis the same. In another implementation, the duration of each of the OFDMsub-channel blocks need not be the same.

In another embodiment, a downlink OFDMA signal includes one or more OFDMsub-channel blocks that conform to a defined communication protocolspecification, such as the IEEE 802.11ac Standard now in the process ofbeing adopted, so that each OFDM sub-channel block in the OFDMA dataunit forms an OFDM data unit. In some embodiments, information inpreambles of OFDM sub-channel blocks of an OFDMA data unit indicate orsignals that each OFDM sub-channel block is part of an OFDMA data unit.In an embodiment, such signaling information is included in a suitablepreamble field such as a field that is the same as or similar to theL-SIG field and/or the HT-SIG field specified in the IEEE 802.11a andIEEE 802.11n Standards.

In some embodiments, client stations respond with an acknowledgmentsignal (ACK) or a negative ACK signal (NAK) after the AP transmits eachdownlink OFDMA data unit or after the AP transmits a plurality ofdownlink OFDMA data units (referred to as “Block ACK”). FIG. 6 is adiagram illustrating the transmission of a downlink OFDMA data unit 200by an AP, and the transmission of ACKs 204 by client stations inresponse to the downlink OFDMA data unit 200, according to anembodiment. In the scenario illustrated in FIG. 6, four client stationssuccessfully received data transmitted in the downlink OFDMA data unit200. In response, each of the four client stations transmits an ACK 204simultaneous with the transmission of the other ACKs 204. The ACKs aretransmitted after a short inter-frame space (SIFS) interval. In the IEEE802.11n Standard, SIFS is specified as 16 microseconds, but any suitableSIFS period can be utilized, depending on the particular implementation.In an embodiment, the downlink OFDMA data unit 200 and the ACKs 204 aretransmitted in a time period reserved for OFDMA transmissions in theWLAN. According to an embodiment, client stations transmit ACKs/NAKs byan uplink OFDMA data unit, which will be discussed in more detail below.Each client station transmits the ACK 204 in a different OFDMsub-channel block.

In one embodiment, each client station determines when to transmit anACK/NAK based on a determined duration of the OFDMA data unit 200. Asdiscussed above with respect to FIG. 4, the AP can provide informationin the OFDMA data unit 200 that indicates the duration of the OFDMA dataunit 200, and a client station can use this information to determinewhen to transmit the ACK 204. In another embodiment, the AP assigns atime slot to the client stations in which each client station cantransmit an ACK/NAK. For example, a MAC unit in the AP can signal, in anOFDMA data unit previous to the OFDMA data unit 200, the time period inwhich the client stations are to transmit ACKs/NAKs.

FIG. 7 is a diagram illustrating the transmission of a downlink OFDMAdata unit 250 by an AP, and the transmission of ACKs 254 by clientstations in response to the downlink OFDMA data unit 250, according toan embodiment. In the scenario illustrated in FIG. 7, four clientstations successfully received data transmitted in the downlink OFDMAdata unit 250. In response, each of the four client stations transmitsan ACK 254 at different specified times. The downlink OFDMA data unit250 and the ACKs are transmitted in a time period reserved for OFDMA. AMAC unit of the AP has signaled each of the client stations providingeach client station with an indication of the time at which the clientstation can transmit an ACK/NAK. For example, according to anembodiment, the MAC unit of the AP provides ACK/NAK time slotinformation to the client stations when providing information regardingthe reserved time period for OFDMA.

The ACKs are spaced by SIFS intervals. In an embodiment, the downlinkOFDMA data unit 250 and the ACKs 254 are transmitted in a time periodreserved for OFDMA transmissions in the WLAN. According to anembodiment, client stations transmit ACKs/NAKs by an uplink OFDMA dataunit, which is discussed in more detail below. Each client stationtransmits the ACK 254 in a different OFDM sub-channel block.

In an embodiment, the AP assigns the time slots to the client stationsin which each client station can transmit the ACKs/NAKs. For example, aMAC unit in the AP can signal, in an OFDMA data unit previous to theOFDMA data unit 250, the time period in which a client stations is totransmit an ACK/NAK.

In another embodiment, ACKs/NAKs are transmitted by the client stationsafter receiving a plurality of downlink OFDMA data units (referred to as“Block ACK”). In this embodiment, a client station determines when totransmit a Block ACK based on determining a duration of a downlink OFDMAdata unit or transmits in a time slot assigned by the AP, for example.

In an embodiment, the downlink OFDMA signal is configured to be receivedand decoded by a legacy client station (e.g., a client stationconfigured to communicate according to the IEEE 802.11a Standard and/orthe IEEE 802.11n Standard). In an embodiment, the AP does not signal toat least the legacy client stations that an OFDMA data unit is an OFDMAsignal (as opposed to an OFDM data unit according to the legacy protocol(e.g., the IEEE 802.11a Standard and/or the IEEE 802.11n Standard). Inan embodiment, at least OFDM sub-channel blocks corresponding to legacyclient stations have the same duration as the downlink OFDMA signal sothat ACKs/NAKs transmitted by the legacy client station occur atappropriate times with respect to the OFDMA data unit.

FIG. 8 is a flow diagram of an example method 300 that is implemented byan AP in a WLAN, according to an embodiment. At block 304, a pluralityof different OFDM sub-channel blocks are assigned to a plurality ofdifferent client stations. At block 308, a plurality of independent datastreams (i.e., the streams include different data) are received, whereineach data stream corresponds to a respective client station, and thedata streams are to be transmitted to the client stations. At block 312,downlink OFDM data units are generated such that the plurality ofindependent data streams are modulated in respective OFDM sub-channelblocks. In an embodiment, generating downlink OFDM data units comprisesincluding an indication in a downlink OFDM data unit that the data unitis an OFDMA data unit (i.e., the data unit includes multiple OFDMsub-channel blocks corresponding to different client stations. In anembodiment, generating downlink OFDM data units comprises including anindication in an OFDM sub-channel block of a duration of a downlink OFDMdata unit (i.e., an indication of a duration of the longest durationOFDM sub-channel block in the OFDMA data unit) separate from anindication of the duration of the OFDM sub-channel block. According toan embodiment, the indication of the duration of the downlink OFDM dataunit includes an indication of a rate and an indication of a lengthcorresponding to the longest duration OFDM sub-channel block in theOFDMA data unit.

At block 316, the AP transmits the OFDM data units generated at block312.

FIG. 9 is a flow diagram of an example method 350 that is implemented byan AP in a WLAN, according to an embodiment. In an embodiment, themethod 350 is implemented in conjunction with the method 300 of FIG. 8.

At block 354, the AP determines a time period that is reserved fordownlink OFDMA signals. In one embodiment, the AP also determines a timeor times at which client stations can transmit ACKs/NAKs or Block ACKsin response to downlink OFDMA data units.

At block 358, the AP transmits to the client stations data indicative ofthe time period determined at block 354. In one embodiment, the AP alsotransmits data indicative of the time or times at which client stationscan transmit ACKs/NAKs or Block ACKs in response to downlink OFDMA dataunits.

FIG. 10 is a block diagram of an example PHY unit 400 of an AP,according to an embodiment. Referring again to FIG. 1, the PHY unit 20of the AP 14 includes the PHY unit 400 of FIG. 10, in an embodiment.

The PHY unit 400 includes a plurality of processing blocks 404. In anembodiment, each processing block 404 performs forward error correction(FEC) encoding, modulation, and spatial mapping functions in a mannerthe same as or similar to such functions described in the IEEE 802.11aStandard and/or the IEEE 802.11n Standard. In FIG. 10, four processingblocks 404 are illustrated. In other embodiments, a different number ofprocessing blocks 404 are included. For example, in one embodiment, asingle processing block 404 is time-shared to process multiple datastreams received in parallel.

The processing blocks 404 receive a plurality of independent datastreams to be transmitted to a plurality of client devices. In theembodiment of FIG. 10, each processing block 404 processes a differentone of the independent data streams and generates a plurality ofconstellation points corresponding to a plurality of OFDM sub-channels.

Outputs of the processing blocks 404 are provided to a mapping unit 408.The mapping unit 408 concatenates constellation points from theprocessing blocks 404 into a larger width OFDM symbol. For example, ifthe output of each processing block 404 corresponds to a 20 MHz wide(64-point inverse fast Fourier transform (IFFT)) OFDM symbol, then themapping unit 408 concatenates the outputs of the processing blocks 404into an 80 MHz wide (256-point IFFT). As another example, if the outputof each processing block 404 corresponds to a 40 MHz wide (128-pointIFFT) OFDM symbol, then the mapping unit 408 concatenates the outputs ofthe processing blocks 404 into a 160 MHz wide (512-point IFFT).

An IFFT unit 412 generates a time-domain signal from the output of themapping unit 408. In an embodiment, the IFFT unit 412 has a width largerthan in a typical AP configured to implement the IEEE 802.11a Standardand/or the IEEE 802.11n Standard. In one embodiment, the IFFT unit 412implements a 256-point IFFT. In another embodiment, the IFFT unit 412implements a 512-point IFFT. In another embodiment, the IFFT unit 412implements a suitable width IFFT other than a 256-point IFFT or a512-point IFFT.

A digital processing and digital-to-analog converter (DAC) block 416processes the output of the IFFT unit 412 and generates an analogsignal. In an embodiment, the digital processing and DAC block 416includes a guard interval insertion unit. In another embodiment, thedigital processing and DAC block 416 includes a windowing unit to smoothedges of each OFDM symbol. In an embodiment, the digital processing andDAC block 416 is configured to process signals with a larger bandwidthas compared to a similar processing block in a typical AP configured toimplement the IEEE 802.11a Standard and/or the IEEE 802.11n Standard. Inone embodiment, the digital processing and DAC block 416 is configuredto process signals with a bandwidth of 80 MHz. In another embodiment,the digital processing and DAC block 416 is configured to processsignals with a bandwidth of 160 MHz. In another embodiment, the digitalprocessing and DAC block 416 is configured to process signals with abandwidth different than 80 MHz or 160 MHz.

A radio frequency (RF) modulation block 420 generally upconverts theoutput of the digital processing and DAC block 416 to generate an RFsignal, which is transmitted by an antenna 424. In an embodiment, the RFmodulation block 420 is configured to process signals with a largerbandwidth as compared to a similar RF block in a typical AP configuredto implement the IEEE 802.11a Standard and/or the IEEE 802.11n Standard.In one embodiment, the RF modulation block 420 is configured to processsignals with a bandwidth of 80 MHz. In another embodiment, the RFmodulation block 420 is configured to process signals with a bandwidthof 160 MHz. In another embodiment, the RF modulation block 420 isconfigured to process signals with a bandwidth different than 80 MHz or160 MHz.

In an embodiment, the PHY unit 400 is a sub-unit in a MIMO PHY unit. Inthis embodiment, the MIMO PHY unit includes a plurality of digitalprocessing and DAC blocks 416 and a plurality of RF modulation blocks420 corresponding to a plurality of antennas 424. In another embodiment,the MIMO PHY unit includes a plurality of mapping units 408 and aplurality of IFFT units 412 corresponding to a plurality of transmitchains. In this embodiment, each processing block 404 generates aplurality of outputs corresponding to a plurality of spatially mappedtransmit chain signals. In another embodiment, the MIMO PHY unitincludes a beamforming unit.

FIG. 11 is a block diagram of an example PHY unit 450 of an AP,according to another embodiment. Referring again to FIG. 1, the PHY unit20 of the AP 14 includes the PHY unit 450 of FIG. 11, in an embodiment.

The PHY unit 450 includes the plurality of processing blocks 404 of FIG.10. A plurality of IFFT units 454 generate time-domain signals from theoutputs of the processing blocks 404. In an embodiment, each IFFT unit454 has a width such as in a typical AP configured to implement the IEEE802.11a Standard and/or the IEEE 802.11n Standard. In one embodiment,each IFFT unit 454 implements a 64-point IFFT. In another embodiment,each IFFT unit 454 implements a 128-point IFFT. In another embodiment,each IFFT unit 454 implements a suitable width IFFT other than a64-point IFFT or a 128-point IFFT.

A plurality of digital processing and DAC blocks 458 process the outputsof the IFFT units 454 and generate corresponding analog signals. In anembodiment, each digital processing and DAC block 458 includes a guardinterval insertion unit. In another embodiment, each digital processingand DAC block 458 includes a windowing unit to smooth edges of each OFDMsymbol. In an embodiment, each digital processing and DAC block 458 isconfigured to process signals having a bandwidth such as in a typical APconfigured to implement the IEEE 802.11a Standard and/or the IEEE802.11n Standard. In one embodiment, each digital processing and DACblock 458 is configured to process signals with a bandwidth of 20 MHz.In another embodiment, each digital processing and DAC block 458 isconfigured to process signals with a bandwidth of 40 MHz. In anotherembodiment, each digital processing and DAC block 458 is configured toprocess signals with a bandwidth different than 20 MHz or 40 MHz.

A plurality of RF modulation blocks 462 generally upconvert the outputsof the digital processing and DAC block 458 to generate RF signals,which are transmitted by respective antennas 466. In an embodiment, eachRF modulation block 462 is configured to process signals having abandwidth such as in a typical AP configured to implement the IEEE802.11a Standard and/or the IEEE 802.11n Standard. In one embodiment,each RF modulation block 462 is configured to process signals with abandwidth of 20 MHz. In another embodiment, each RF modulation block 462is configured to process signals with a bandwidth of 40 MHz. In anotherembodiment, each RF modulation block 462 is configured to processsignals with a bandwidth different than 20 MHz or 40 MHz.

In an embodiment, the PHY unit 450 is a sub-unit in a MIMO PHY unit. Inone embodiment, the MIMO PHY unit includes an additional set of one ormore of the IFFT units 454, the digital processing and DAC blocks 458,and the RF modulation blocks 462 for each of a plurality of transmitchains. In one embodiment, the MIMO PHY unit includes a beamformingunit.

In one embodiment, the AP utilizes a single MAC address for thedifferent OFDM sub-channel blocks. In an embodiment, the AP includes aMAC unit that includes a plurality of transmit/receive processing blockscorresponding to the plurality of client devices with which the AP iscommunicating using OFDMA signals such as described above. The pluralityof transmit/receive processing blocks in the MAC unit process theindependent data streams simultaneously and/or in parallel.

In an embodiment, a client station that supports OFDMA signaling asdescribed above includes a modified PHY unit (as compared to a PHY unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified PHY unit is configuredto determine when a received data unit is within an OFDMA data unit,according to an embodiment. For instance, the PHY unit examines theL-SIG and/or HT-SIG “reserved” bits to detect an OFDMA data unit, in anembodiment. As another example, the modified PHY unit is configured todetermine when an OFDMA data unit will end, as opposed to an OFDMsub-channel block within the OFDMA data unit that corresponds to theclient station, according to an embodiment. For instance, the PHY unitexamines the Length and Rate subfields in the L-SIG field to determine aduration of the OFDMA data unit for purposes of determining when totransmit an ACK/NAK, in an embodiment.

In an embodiment, a client station that supports OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto interpret MAC signals from the AP regarding when the client cantransmit ACKs/NAKs or Block ACKs, according to an embodiment. As anotherexample, the modified MAC unit is configured to interpret MAC signalsfrom the AP regarding periods reserved for OFDMA signals.

In an embodiment, a combination of PHY and MAC signaling is utilized forindicating OFDMA data units, the duration of OFMDA data units, and/orreserved time slots for OFDMA signals. In this embodiment, a clientstation that supports OFDMA signaling as described above includes amodified PHY unit and a modified MAC unit, such as described above.

FIG. 12 is a diagram illustrating communications in a WLAN 470 duringthree time periods: a first CSMA period 474, an OFDMA time period 478,and a second CSMA period 482. In FIG. 12, time progresses from left toright so that the first CSMA period 474 occurs first, the OFDMA timeperiod 478 occurs second, and the second CSMA period 482 occurs third.The WLAN includes an AP, a plurality of legacy client stations (LCs),and a plurality of OFDMA client stations (OC).

In the first CSMA period 474, the AP transmits a legacy downlink singleto one of the LCs. The OFDMA period 478 is reserved for OFDMA signaltransmissions. Thus, in the OFDMA period 478, the AP transmits adownlink OFDMA signal to a plurality of OCs. The downlink OFDMA signalincludes a plurality of OFDM sub-channel blocks corresponding to theplurality of OCs. In the OFDMA period 478, the plurality of OCs alsotransmit ACKs/NAKs (not shown) in response to the downlink OFDMA signal,according to an embodiment. In the second CSMA period 482, an LCtransmits a legacy uplink transmission to the AP.

Embodiments of a PHY frame format for uplink OFDMA signals will now bedescribed. In the following embodiments, OFDM sub-channel blocks have aformat substantially similar to the PHY format specified in the IEEE802.11n Standard. In other embodiments, OFDM sub-channel blocks have aformat substantially similar to another communication protocol such asthe PHY format specified in the IEEE 802.11a Standard or a communicationprotocol not yet standardized.

An uplink OFDMA signal comprises a plurality of OFDM sub-channel blocks,a plurality of which are transmitted by different client stations. Inone embodiment, each OFDM sub-channel block substantially conforms tothe “mixed mode” format as specified in the IEEE 802.11n Standard. Inanother embodiment each OFDM sub-channel block substantially conforms tothe “Green field” format as specified in the IEEE 802.11n Standard. Inanother embodiment, the OFDM sub-channel blocks in an uplink OFDMA dataunit are mixture of “mixed mode” and “Green field” substantiallyformatted data units.

In one embodiment, an uplink OFDMA data unit with mixed mode OFDMsub-channel blocks transmitted by the plurality of clients has a formatthe same as or similar to the format illustrated in FIG. 4. According toone embodiment, the L-SIG “reserved” bit is not set to indicate an OFDMAdata unit. According to another embodiment, each client station sets theL-SIG “reserved” bit if the client station is aware that the OFDMsub-channel block that the client station is transmitting is part of anuplink OFDMA data unit. According to another embodiment, each clientstation does not set the Length and Rate subfields in the L-SIG fielddifferently than when transmitting a CSMA signal. According to anotherembodiment, each client station sets Length and Rate subfields in theL-SIG field to correspond to the duration of the uplink OFDMA data unitif the client station is aware of the duration of the uplink OFDMA dataunit.

In one embodiment, the AP reserves a time period for transmission ofuplink OFDMA signals. In this embodiment, the AP transmits informationregarding the starting time, ending time, and/or duration of thereserved time period to the client stations.

According to an embodiment, an AP capable of receiving an uplink OFDMAsignal includes an RF demodulation block, an analog-to-digital converter(ADC) and processing block, and an FFT unit that are configured toprocess signals with a larger bandwidth as compared to similar blocks ina typical AP configured to implement the IEEE 802.11a Standard and/orthe IEEE 802.11n Standard. In one embodiment, these blocks areconfigured to process signals with a bandwidth of 80 MHz. In anotherembodiment, these blocks are configured to process signals with abandwidth of 160 MHz. In another embodiment, these blocks are configuredto process signals with a bandwidth different than 80 MHz or 160 MHz.

In another embodiment, an AP capable of receiving an uplink OFDMA signalincludes a plurality of RF demodulation blocks, a plurality of ADC andprocessing blocks, and a plurality of FFT units that are configured toprocess signals process signals having a bandwidth such as in a typicalAP configured to implement the IEEE 802.11a Standard and/or the IEEE802.11n Standard. In one embodiment, each such block is configured toprocess signals with a bandwidth of 20 MHz. In another embodiment, eachsuch block is configured to process signals with a bandwidth of 40 MHz.In another embodiment, each such block is configured to process signalswith a bandwidth different than 20 MHz or 40 MHz. In these embodiments,the plurality of blocks operate in parallel to process each OFDMsub-channel block, which has a smaller bandwidth than the uplink OFDMAsignal, in parallel.

In one embodiment, the AP utilizes a single MAC address for receivingdifferent OFDM sub-channel blocks. In an embodiment, the AP includes aMAC unit that includes a plurality of receive processing blockscorresponding to the plurality of client devices with which the AP iscommunicating using OFDMA signals such as described above. The pluralityof receive processing blocks in the MAC unit process the independentdata streams received from the client stations simultaneously and/or inparallel.

In an embodiment, an AP that supports uplink OFDMA signaling asdescribed above includes a modified PHY unit (as compared to a PHY unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified PHY unit is configuredto operate at a wider bandwidth as described above, according to anembodiment.

In an embodiment, an AP that supports uplink OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto determine when the AP can transmit ACKs/NAKs or Block ACKs, accordingto an embodiment. As another example, the modified MAC unit isconfigured to reserve time periods for uplink OFDMA signals.

In an embodiment, a legacy AP is capable of receiving and decoding datatransmitted in an OFDM sub-channel block by a client station as part ofan uplink OFDMA signal.

In an embodiment, a client that supports uplink OFDMA signaling asdescribed above merely implements a PHY data unit that conforms to theIEEE 802.11a Standard and/or the IEEE 802.11n Standard. In anotherembodiment, a client that supports uplink OFDMA signaling as describedabove includes a modified PHY unit (as compared to a PHY unit configuredto operate according to the IEEE 802.11a Standard and/or the IEEE802.11n Standard). For example, the modified PHY unit is configured toperform PHY signaling regarding uplink OFDMA.

In an embodiment, a client that supports uplink OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto determine when the AP can transmit uplink signals with respect to areserved time period for uplink OFDMA, according to an embodiment.

FIG. 13 is a diagram illustrating the transmission of an uplink OFDMAdata unit 500 by a plurality of client stations, and the transmission ofACKs 504 by the AP in response to the uplink OFDMA data unit 500,according to an embodiment. In the scenario illustrated in FIG. 13, fourclient stations simultaneously transmit respective OFDM sub-channelblocks 508 to the AP. The OFDM sub-channel blocks 508 form the uplinkOFDMA data unit 500.

In the scenario illustrated in FIG. 13, the AP successfully receivedeach of the OFDM sub-channel blocks 508. In response, the AP transmitsan OFDMA data unit that comprises ACKs 504 corresponding to differentOFDM sub-channel blocks. In an embodiment, the OFDMA data unit thatcomprises the ACKs 504 has a format the same as or similar to a downlinkOFDMA data unit as described with respect to FIG. 5, the same as orsimilar to a downlink OFDMA data unit as described with respect to FIG.6, or has another suitable format.

The uplink OFDMA data unit 500 and the ACKs 504 are transmitted in atime period reserved for uplink OFDMA. A MAC unit of the AP has signaledeach of the client stations providing each client station with anindication of the time at which the client station can transmit thecorresponding OFDM sub-channel block 508. For example, according to anembodiment, the MAC unit of the AP provides uplink OFDMA time slotinformation to the client stations.

The ACKs are spaced from the OFDMA data unit 500 by a SIFS intervals. Inan embodiment, a MAC unit of a client station is configured to wait,after the corresponding OFDM sub-channel block, longer than the SIFSinterval for an ACK/NAK from the AP. In an embodiment, the MAC unit ofthe client station is configured to wait for a time out period forretransmission if an ACK/NAK from the AP is not received, wherein thetime out period is longer than the SIFS interval.

In an embodiment, the AP transmits Block ACKs after receiving severaluplink OFDMA data units.

According to an embodiment, the AP transmits a synchronization signal tothe client stations to help the client stations synchronize fortransmitting an uplink OFDMA signal. In an embodiment, thesynchronization signal is transmitted to the client stations as adownlink OFDMA signal. FIG. 14 is a diagram illustrating thetransmission of the uplink OFDMA data unit 500 being preceded by the APtransmitting downlink synchronization signals 520, according to anembodiment. In an embodiment, the synchronization signals 520 aretransmitted to the client stations as a downlink OFDMA signal. Thesynchronization signals 520 have the same duration, according to anembodiment.

In the embodiment according to FIG. 14, each client station transmitsthe corresponding OFDM sub-channel block 508 at a determined timeduration after receiving the corresponding synchronization signal 520.

FIG. 15 is a diagram illustrating communications in a WLAN 550 duringthree time periods: a first CSMA period 554, an OFDMA time period 558,and a second CSMA period 562. In FIG. 15, time progresses from left toright so that the first CSMA period 554 occurs first, the OFDMA timeperiod 558 occurs second, and the second CSMA period 562 occurs third.The WLAN includes an AP, a plurality of legacy client stations (LCs),and a plurality of OFDMA client stations (OC).

In the first CSMA period 554, the AP transmits a legacy downlink singleto one of the LCs. The OFDMA period 558 is reserved for uplink OFDMAsignal transmissions. Thus, in the OFDMA period 558, a plurality of OCstransmit an uplink OFDMA signal to the AP. The uplink OFDMA signalincludes a plurality of OFDM sub-channel blocks corresponding to theplurality of OCs. In the OFDMA period 558, the AP also transmitsACKs/NAKs (not shown) in response to the uplink OFDMA signal, accordingto an embodiment. According to an embodiment, in the OFDMA period 558,the AP also transmits synchronization signals (not shown) prior to theuplink OFDMA signal. In the second CSMA period 562, an LC transmits alegacy uplink transmission to the AP.

According to some embodiments, the above discussed OFDMA techniques areutilized in combination with simultaneous downlink transmission (SDT)techniques and simultaneous uplink transmission (SUT) techniquesdescribed in U.S. patent application Ser. No. 14/175,526, entitled“Access Point with Simultaneous Downlink Transmission of IndependentData for Multiple Client Stations,” filed on Jul. 18, 2008, and U.S.patent application Ser. No. 14/175,501, entitled “Wireless Network withSimultaneous Uplink Transmission of Independent Data from MultipleClient Stations,” filed on Jul. 18, 2008. Both of U.S. patentapplication Ser. No. 14/175,526 and U.S. patent application Ser. No.14/175,501 are hereby expressly incorporated by reference herein intheir entireties.

FIG. 16 is a flow diagram of an example method 600 that is implementedby an AP in a WLAN, according to an embodiment. At block 604, aplurality of different OFDM sub-channel blocks are assigned to aplurality of different client stations. At block 308, OFDM data unitsare received, wherein each OFDM data unit comprises a plurality ofdifferent OFDM sub-channel blocks transmitted by the plurality of clientstations simultaneously. In an embodiment, a plurality of independentdata streams are modulated in respective OFDM sub-channel blocks.

At block 612, the plurality of independent data streams are demodulated.

In another embodiment, the method includes transmitting asynchronization signal from the AP prior to receiving each OFDM signalat block 608.

FIG. 17 is a flow diagram of an example method 650 that is implementedby an AP in a WLAN, according to an embodiment. In an embodiment, themethod 650 is implemented in conjunction with the method 600 of FIG. 16.

At block 654, the AP determines a time period that is reserved foruplink OFDMA signals. At block 658, the AP transmits to the clientstations data indicative of the time period determined at block 654.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for transmitting to a plurality ofclient stations in a wireless local area network (WLAN), the methodcomprising: assigning, at an access point (AP) device, respective blocksof orthogonal frequency division multiplexing (OFDM) tones to theplurality of client stations for an orthogonal frequency divisionmultiple access (OFDMA) data unit; receiving, at the AP device,respective independent data for the plurality of client stations;generating, at the AP device, a preamble of the OFDMA data unit toinclude: respective legacy preamble portions in respective sub-channels,wherein each legacy preamble portion includes a legacy signal field thatindicates a duration of the OFDMA data unit, and a non-legacy preambleportion; generating, at the AP device, a data portion of the OFDMA dataunit to include respective independent data for respective clientstations, the respective independent data included within the respectiveblocks of OFDM tones; and transmitting, by the AP device, the OFDMA dataunit.
 2. The method of claim 1, wherein each legacy signal fieldincludes a rate subfield and a length subfield set to values thatindicate the duration of the OFDMA data unit.
 3. The method of claim 1,further comprising: sequentially receiving, at the AP device,acknowledgment packets from respective client stations among theplurality of client stations, the acknowledgment packets acknowledgingreceipt of respective independent data within the OFDMA data unit. 4.The method of claim 3, wherein: the acknowledgment packets are receivedvia respective subchannels.
 5. The method of claim 1, wherein: the OFDMAdata unit is a downlink OFDMA data unit; the method further comprises:receiving, at the AP device, an uplink OFDMA transmission from multipleclient stations; and the uplink OFDMA transmission includesacknowledgments from multiple client stations among the plurality ofclient stations, the acknowledgments acknowledging receipt of respectiveindependent data within the OFDMA data unit.
 6. The method of claim 5,wherein: the acknowledgments are received via respective subchannels,wherein each acknowledgment spans only the respective subchannel.
 7. Themethod of claim 1, wherein each subchannel has a bandwidth of 20 MHz. 8.The method of claim 1, wherein: assigning the respective blocks of OFDMtones comprises i) assigning a first block of OFDM tones to a firstclient station, and ii) assigning a second block of OFDM tones to asecond client station; a first bandwidth corresponding to the firstblock of OFDM tones is wider than a second bandwidth corresponding tothe first block of OFDM tones; the data portion of the OFDMA data unitis generated to include i) first independent data for the first clientstation within the first block of OFDM tones, and ii) second independentdata for the second client station within the second block of OFDMtones.
 9. The method of claim 8, wherein: the first bandwidthcorresponding to the first block of OFDM tones is 40 MHz; and the secondbandwidth corresponding to the second block of OFDM tones is 20 MHz. 10.A wireless communication device, comprising: a wireless local areanetwork (WLAN) network interface device associated with an access point(AP) device of a WLAN, the WLAN network interface device having: one ormore integrated circuit (IC) devices, and one or more transceivers;wherein the one or more IC devices are configured to: assign respectiveblocks of orthogonal frequency division multiplexing (OFDM) tones to theplurality of client stations for an orthogonal frequency divisionmultiple access (OFDMA) data unit, receive respective independent datafor the plurality of client stations, generate a preamble of the OFDMAdata unit to include: a respective legacy preamble portion in eachsub-channel of a plurality of subchannels, wherein each legacy preambleportion includes a legacy signal field that indicates a duration of theOFDMA data unit, and a non-legacy preamble portion; wherein the one ormore IC devices are further configured to: generate a data portion ofthe OFDMA data unit to include respective independent data forrespective client stations, the respective independent data includedwithin the respective blocks of OFDM tones, and control the one or moretransceivers to transmit the OFDMA data unit.
 11. The wirelesscommunication device of claim 10, wherein the one or more IC devices arefurther configured to generate each legacy signal field to include arate subfield and a length subfield set to values that indicate theduration of the OFDMA data unit.
 12. The wireless communication deviceof claim 10, wherein the WLAN network interface device is configured to:sequentially receive acknowledgment packets from respective clientstations among the plurality of client stations, the acknowledgmentpackets acknowledging receipt of respective independent data within theOFDMA data unit.
 13. The wireless communication device of claim 12,wherein: the acknowledgment packets are received via respectivesubchannels.
 14. The wireless communication device of claim 10, wherein:the OFDMA data unit is a downlink OFDMA data unit; the WLAN networkinterface device is further configured to: receive an uplink OFDMAtransmission from multiple client stations; and the uplink OFDMAtransmission includes acknowledgments from multiple client stationsamong the plurality of client stations, the acknowledgmentsacknowledging receipt of respective independent data within the OFDMAdata unit.
 15. The wireless communication device of claim 14, wherein:the acknowledgments are received via respective subchannels, whereineach acknowledgment spans only the respective subchannel.
 16. Thewireless communication device of claim 10, wherein each subchannel has abandwidth of 20 MHz.
 17. The wireless communication device of claim 10,wherein: the one or more IC devices are further configured to i) assigna first block of OFDM tones to a first client station, and ii) assign asecond block of OFDM tones to a second client station; a first bandwidthcorresponding to the first block of OFDM tones is wider than a secondbandwidth corresponding to the first block of OFDM tones; the one ormore IC devices are further configured to generate the data portion ofthe OFDMA data unit to include i) first independent data for the firstclient station within the first block of OFDM tones, and ii) secondindependent data for the second client station within the second blockof OFDM tones.
 18. The wireless communication device of claim 10,wherein the one or more transceivers are implemented at least partiallyon the one or more IC devices.
 19. A method for communicating with aplurality of client stations in a wireless local area network (WLAN),the method comprising: transmitting, by an access point (AP) device of awireless local area network (WLAN), a synchronization signal to prompt aplurality of client stations of the WLAN to transmit as part of anuplink orthogonal frequency division multiple access (OFDMA)transmission at a time that begins a defined time period after an end ofthe synchronization signal; and subsequent to transmitting thesynchronization signal, receiving, at the AP device, the uplink OFDMAtransmission from the plurality of client stations, wherein the OFDMAtransmission is responsive to the synchronization signal, and whereinthe uplink OFDMA transmission includes: respective legacy preambleportions in respective sub-channels, wherein each legacy preambleportion includes a legacy signal field that indicates a duration of theuplink OFDMA transmission, a non-legacy preamble portion, and respectiveindependent data from respective client stations among the plurality ofclient stations, the respective independent data included withinrespective blocks of orthogonal frequency division multiplex (OFDM)tones.
 20. The method of claim 19, wherein each legacy signal fieldincludes a rate subfield and a length subfield set to values thatindicate the duration of the uplink OFDMA transmission.
 21. The methodof claim 19, further comprising: transmitting, by the AP device,respective acknowledgments in respective subchannels in response toreceiving the uplink OFDMA transmission, the respective acknowledgmentsacknowledging receipt of respective data within the uplink OFDMAtransmission; wherein each acknowledgment spans only the respectivesubchannel.
 22. The method of claim 21, wherein: transmitting therespective acknowledgments comprises transmitting, by the AP device, adownlink OFDMA data unit that includes the respective acknowledgments.23. The method of claim 19, wherein: each subchannel has a bandwidth of20 MHz.
 24. The method of claim 19, further comprising: assigning, atthe AP device, the respective blocks of OFDM tones to respective clientstations.
 25. A wireless communication device, comprising: a wirelesslocal area network (WLAN) network interface device associated with anaccess point (AP) device of a WLAN, the WLAN network interface devicehaving: one or more integrated circuit (IC) devices, and one or moretransceivers; wherein the one or more IC devices are configured to:control the one or more transceivers to transmit a synchronizationsignal to prompt a plurality of client stations of a WLAN to transmit aspart of an uplink orthogonal frequency division multiple access (OFDMA)transmission at a time that begins a defined time period after an end ofthe synchronization signal; wherein the WLAN network interface device isconfigured to: subsequent to transmitting the synchronization signal,receive the uplink OFDMA transmission from the plurality of clientstations, wherein the OFDMA transmission is responsive to thesynchronization signal, and wherein the uplink OFDMA transmissionincludes: respective legacy preamble portions in respectivesub-channels, wherein each legacy preamble portion includes a legacysignal field that indicates a duration of the uplink OFDMA transmission,a non-legacy preamble portion, and respective independent data fromrespective client stations among the plurality of client stations, therespective independent data included within respective blocks oforthogonal frequency division multiplex (OFDM) tones.
 26. The wirelesscommunication device of claim 25, wherein each legacy signal fieldincludes a rate subfield and a length subfield set to values thatindicate the duration of the uplink OFDMA transmission.
 27. The wirelesscommunication device of claim 25, wherein the one or more IC devices arefurther configured to: control the one or more transceivers to transmitrespective acknowledgments in respective subchannels in response toreceiving the uplink OFDMA transmission, the respective acknowledgmentsacknowledging receipt of respective data within the uplink OFDMAtransmission; wherein each acknowledgment spans only the respectivesubchannel.
 28. The wireless communication device of claim 27, whereinthe one or more IC devices are further configured to: transmit adownlink OFDMA data unit that includes the respective acknowledgments.29. The wireless communication device of claim 25, wherein the one ormore IC devices are further configured to: assign the respective blocksof OFDM tones to respective client stations.
 30. The wirelesscommunication device of claim 25, wherein the one or more transceiversare implemented at least partially on the one or more IC devices.